Well you have a archive program that comes with your desktop more then likely. For example with my Gnome dekstop we have a thing called "file roller" that opens up a window with the contents of archive files displayed.
But for stuff like that I generally use command line. You have a unzip command, and a zip command for making zip files. However you are more likely to run into "tarballs", which are tar files that were compressed using gzip or bzip2. Tars are files that contain a bunch of directories and files, but instead of have it in a bunch of individual files and directories, it's squished into one big file. Then you run a compression utility to make it take up less space and to save bandwidth.
So say you have a file "hard.tar.gz" or "hard.tgz" (because Win machines don't handle multiple . very well.) You go:
tar zxfv hard.tar.gz
and that will uncompress it.
With a bzip2'd tar file you go:
tar jxfv hard.tar.bz2
People use that instead of zip because it makes smaller files, and works better in a Unix-like enviroment. Of course if you don't want to deal with command line stuff you can just use whatever GUI archive tool is aviable by default. Like Fileroller.
For Anti-virus, it's unneeded.
For Defrag, it's unneeded.
Although their is anti-virus stuff aviable, it's used mostly in Linux servers that serve files to Windows Machines to make sure that you aren't spreading infected files. Windows Viruses don't affect Linux, but you can still send attatchments that you receive from a infected windows box to another windows box.
fprot is free for Linux home users
But you don't have to worry about viruses infecting you on a Linux box.
here is a good website for various howtos and stuff. Check out the Guide section, there is a introduction guide for Bash shell (the command line), so you don't have to be afraid of it. Their is a introduction guide for Linux, so it will explain some basics on how the OS itself works. Then their are more in-depth guides like bash scripting guide and Linux administrator guide.
Otherwise just use
Google. (special search for Linux) for linux stuff. Just search for what you want to find out about, you'll find something. Also pay attention to the dates, some stuff is out of date and not so usefull to use.